Method and apparatus for transmitting reference signal in multi-antenna system

ABSTRACT

A method for transmitting a reference signal in a multi-antenna system is provided. The method includes: selecting at least one orthogonal frequency division multiplexing (OFDM) symbol in a subframe containing a plurality of OFDM symbols; allocating a channel quality indication reference signal (CQI RS) capable of measuring a channel state for each of a plurality of antennas to the selected at least one OFDM symbol; and transmitting the CQI RS, wherein the CQI RS is allocated to an OFDM symbol which does not overlap with an OFDM symbol to which a common reference signal to be transmitted to all user equipments in a cell or a dedicated reference signal to be transmitted to a specific user equipment in the cell is allocated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2010/001789, filed on Mar. 23, 2010,which claims the benefit of earlier filing date and right of priority toKorean Application No. 10-2010-0025968, filed on Mar. 23, 2010, and alsoclaims the benefit of U.S. Provisional Application Ser. Nos. 61/299,354,filed on Jan. 29, 2010, 61/163,874, filed on Mar. 27, 2009, 61/162,684,filed on Mar. 24, 2009, and 61/162,344, filed on Mar. 23, 2009, thecontents of which are all incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for transmitting a referencesignal in a multi-antenna system.

BACKGROUND ART

To maximize performance and communication capacity of a wirelesscommunication system, a multiple input multiple output (MIMO) system hasdrawn attention in recent years. Being evolved from the conventionaltechnique in which a single transmit (Tx) antenna and a single receive(Rx) antenna are used, a MIMO technique uses multiple Tx antennas andmultiple Rx antennas to improve transfer efficiency of data to betransmitted or received. The MIMO system is also referred to as amultiple antenna system. In the MIMO technique, instead of receiving onewhole message through a single antenna path, data segments are receivedthrough a plurality of antennas and are then collected as one piece ofdata. As a result, a data transfer rate can be improved in a specificrange, or a system range can be increased with respect to a specificdata transfer rate.

The MIMO technique includes transmit diversity, spatial multiplexing,and beamforming. The transmit diversity is a technique in which themultiple Tx antennas transmit the same data so that transmissionreliability increases. The spatial multiplexing is a technique in whichthe multiple Tx antennas simultaneously transmit different data so thatdata can be transmitted at a high speed without increasing a systembandwidth. The beamforming is used to add a weight to multiple antennasaccording to a channel condition so as to increase a signal tointerference plus noise ratio (SINR) of a signal. In this case, theweight can be expressed by a weight vector or a weight matrix, which isrespectively referred to as a precoding vector or a precoding matrix.

The spatial multiplexing is classified into single-user spatialmultiplexing and multi-user spatial multiplexing. The single-userspatial multiplexing is also referred to as a single user MIMO(SU-MIMO). The multi-user spatial multiplexing is also referred to as aspatial division multiple access (SDMA) or a multi user MIMO (MU-MIMO).A capacity of a MIMO channel increases in proportion to the number ofantennas. The MIMO channel can be decomposed into independent channels.If the number of Tx antennas is Nt, and the number of Rx antennas is Nr,then the number of independent channels is Ni where Ni≦min{Nt, Mr}. Eachindependent channel can be referred to as a spatial layer. A rankrepresents the number of non-zero eigen-values of the MIMO channel andcan be defined as the number of spatial streams that can be multiplexed.

For the purpose of data transmission/reception, system synchronizationacquisition, channel information feedback, etc., there is a need toestimate an uplink channel or a downlink channel in the wirelesscommunication system. Channel estimation is a process of recovering atransmission signal by compensating for signal distortion in anenvironment where a rapid change occurs due to fading. In general,channel estimation requires a reference signal or a pilot known to boththe transmitter and the receiver.

In the multi-antenna system, each antenna may experience a differentchannel, and thus there is a need to design a deployment structure of areference signal by considering each antenna. Conventionally, when asignal is transmitted from a base station to a user equipment, referencesignals are deployed under the assumption that up to 4 antennas areused. However, a next generation wireless communication system cantransmit a downlink signal by using a more number of antennas, i.e., upto 8 antennas. In this case, how to deploy and transmit the referencesignals needs to be taken into account.

SUMMARY OF INVENTION Technical Problem

The present invention provides a method and apparatus for transmitting areference signal in a multi-antenna system.

Technical Solution

According to an aspect of the present invention, a method fortransmitting a reference signal in a multi-antenna system. The methodincludes: selecting at least one orthogonal frequency divisionmultiplexing (OFDM) symbol in a subframe containing a plurality of OFDMsymbols; allocating a channel quality indication reference signal (CQIRS) capable of measuring a channel state for each of a plurality ofantennas to the selected at least one OFDM symbol; and transmitting theCQI RS, wherein the CQI RS is allocated to an OFDM symbol which does notoverlap with an OFDM symbol to which a common reference signal to betransmitted to all user equipments in a cell or a dedicated referencesignal to be transmitted to a specific user equipment in the cell isallocated.

Advantageous Effects

Reference signals corresponding to a more number of antennas incomparison with the conventional antennas in a multi-antenna system canbe transmitted by being deployed in various manners according toavailable radio resources. That is, the reference signals can betransmitted adaptively according to a situation of a wirelesscommunication system.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a structure of a wireless communication system.

FIG. 2 shows a radio frame structure.

FIG. 3 shows an example of a resource grid for one downlink slot.

FIG. 4 shows a structure of a subframe.

FIG. 5 shows an exemplary structure of a common reference signal (RS)for one antenna.

FIG. 6 shows an exemplary structure of a common RS for two antennas.

FIG. 7 shows an exemplary structure of a common RS for four antennas ina subframe when using a normal cyclic prefix (CP).

FIG. 8 shows an exemplary structure of a common RS for four antennas ina subframe when using an extended CP.

FIG. 9 shows an exemplary structure of a dedicated RS in a subframe whenusing a normal CP.

FIG. 10 shows an exemplary structure of a dedicated RS in a subframewhen using an extended CP.

FIG. 11 shows a method of transmitting a reference signal in amulti-antenna system according to an embodiment of the presentinvention.

FIG. 12 shows an example of deploying a channel quality indicator (CQI)RS to four resource elements in one orthogonal frequency divisionmultiplexing (OFDM) symbol.

FIG. 13 shows examples of deploying two CQI RSs to four resourceelements in one OFDM symbol.

FIG. 14 shows examples of deploying four CQI RSs to four resourceelements in one OFDM symbol.

FIG. 15 shows an example of applying a CQI RS deployment methoddescribed in FIG. 14 to a subframe.

FIG. 16 shows examples of deploying a CQI RS to 6 resource elements inone OFDM symbol.

FIG. 17 shows an example of applying a CQI RS deployment methoddescribed in FIG. 16.

FIG. 18 shows an example in which a CQI RS is transmitted in one OFDMsymbol in a subframe and in which a CQI RS is deployed to 8 resourceelement in a frequency band corresponding to one resource block.

FIG. 19 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which a CQI RS is deployed to 8resource element in a frequency band corresponding to one resourceblock.

FIG. 20 shows an example in which a CQI RS is transmitted in one OFDMsymbol in a subframe and in which two CQI RSs are deployed to 8 resourceelements in a frequency band corresponding to one resource block.

FIG. 21 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which two CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 22 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which four CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 23 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which four CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 24 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which 8 CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 25 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which 8 CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 26 shows an example of applying a CQI RS deployment methoddescribed in FIG. 22 to a subframe.

FIG. 27 shows an example of applying a CQI RS deployment methoddescribed in FIG. 24 to a subframe.

FIG. 28 to FIG. 33 show examples of deploying 8 CQI RSs to 8 resourceelements in a subframe.

FIG. 34 shows examples in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which a CQI RS is deployed to four resourceelements in a frequency band corresponding to one resource block.

FIG. 35 shows examples of deploying two CQI RSs to four resourceelements in two OFDM symbols.

FIG. 36 shows examples of deploying four CQI RSs to four resourceelements in two OFDM symbols.

FIG. 37 shows an example of deploying four CQI RSs to four resourceelements in two OFDM symbols in a subframe.

FIG. 38 shows an example in which a CQI RS is deployed to four resourceelements in two OFDM symbols in a subframe wherein the resource elementsto which the CQI RS is deployed to each OFDM symbol has the samepattern.

FIG. 39 shows an example in which two CQI RSs are deployed to fourresource elements in two OFDM symbols in a subframe

FIG. 40 shows examples for deploying four CQI RSs to four resourceelements in two OFDM symbols in a subframe.

FIG. 41 shows an example in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which a CQI RS is deployed to 8 resourceelements in a frequency band corresponding to one resource block.

FIG. 42 shows other examples for deploying a CQI RS to 8 resourceelements in two OFDM symbols in a subframe.

FIG. 43 shows examples of deploying two CQI RSs to 8 resource elementsin two OFDM symbols in a subframe.

FIG. 44 shows examples of deploying two CQI RSs to 8 resource elementsin two OFDM symbols in a subframe.

FIG. 45 to FIG. 47 show examples of deploying four CQI RSs to 8 resourceelements in two OFDM symbols in a subframe.

FIG. 48 shows an example in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which four CQI RSs are deployed to 8resource elements.

FIG. 49 shows another example in which a CQI RS is transmitted in twoOFDM symbols in a subframe and in which four CQI RSs are deployed to 8resource elements.

FIG. 50 and FIG. 51 show examples in which a CQI RS is transmitted intwo OFDM symbols in a subframe and in which 8 CQI RSs are deployed to 8resource elements.

FIG. 52 to FIG. 64 show examples in which a CQI RS is transmitted in twoOFDM symbols for a resource region including one subframe in a timedomain and 12 subcarriers in a frequency domain and in which 8 CQI RSsare deployed to 8 resource elements.

FIG. 65 shows examples of deploying a CQI RS to 12 resource elements intwo OFDM symbols in a subframe.

FIG. 66 shows examples of deploying a CQI RS to 16 resource elements intwo OFDM symbols in a subframe.

FIG. 67 shows examples of deploying two CQI RSs to 16 resource elementsin two OFDM symbols in a subframe.

FIG. 68 and FIG. 69 show other examples for deploying two CQI RSs to 16resource elements in two OFDM symbols in a subframe.

FIG. 70 and FIG. 71 show examples for deploying four CQI RSs to 16resource elements in two OFDM symbols in a subframe.

FIG. 72 and FIG. 73 show examples for deploying 8 CQI RSs to 16 resourceelements in two OFDM symbols in a subframe.

FIG. 74 shows an example in which a CQI RS is transmitted in two OFDMsymbols for a resource region including one subframe in a time domainand 12 subcarriers in a frequency domain and in which four CQI RSs aredeployed for 16 resource elements.

FIG. 75 shows an example in which a CQI RS is transmitted in two OFDMsymbols for a resource region including one subframe in a time domainand 12 subcarriers in a frequency domain and in which 8 CQI RSs aredeployed for 16 resource elements.

MODE FOR INVENTION

FIG. 1 shows a structure of a wireless communication system. Thewireless communication system may have a network structure of anevolved-universal mobile telecommunications system (E-UMTS). An E-UMTSsystem may also be referred to as a long term evolution (LTE) system.The wireless communication system can be widely deployed to provide avariety of communication services, such as voices, packet data, etc.

Referring to FIG. 1, an evolved-UMTS terrestrial radio access network(E-UTRAN) includes at least one base station (BS) 20 which provides acontrol plane and a user plane.

A user equipment (UE) 10 may be fixed or mobile, and may be referred toas another terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc. The BS 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc. There are one ormore cells within the coverage of the BS 20. The cell is an area inwhich the BS 20 provides a communication service. Interfaces fortransmitting user traffic or control traffic may be used between the BSs20. Hereinafter, a downlink is defined as a communication link from theBS 20 to the UE 10, and an uplink is defined as a communication linkfrom the UE 10 to the BS 20.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC), more specifically, to a mobility management entity (MME)/servinggateway (S-GW) 30. The S1 interface supports a many-to-many relationbetween the BS 20 and the MME/S-GW 30.

Layers of a radio interface protocol between the UE and the network canbe classified into L1 layer (a first layer), L2 layer (a second layer),and L3 layer (a third layer) based on the lower three layers of the opensystem interconnection (OSI) model that is well-known in thecommunication system. The first layer is a physical (PHY) layer. Thesecond layer can be classified into a medium access control (MAC) layer,a radio link control (RLC) layer, and a packet data convergence protocol(PDCP) layer. The third layer is a radio resource control (RRC) layer.

The wireless communication system may be a system based on orthogonalfrequency division multiplexing (OFDM)/orthogonal frequency divisionmultiple access (OFDMA). The OFDM uses a plurality of orthogonalsubcarriers. Further, the OFDM uses an orthogonality between inversefast Fourier transform (IFFT) and fast Fourier transform (FFT). Atransmitter transmits data by performing IFFT on the data. A receiverrestores original data by performing FFT on a received signal. Thetransmitter uses IFFT to combine the plurality of subcarriers, and thereceiver uses FFT to split the plurality of subcarriers.

The wireless communication system may be a multiple antenna system. Themultiple antenna system may be a multiple input multiple output (MIMO)system. The multiple antenna system may be a multiple-inputsingle-output (MISO) system, a single-input single-output (SISO) system,or a single-input multiple-output (SIMO) system. The MIMO system uses aplurality of transmit (Tx) antennas and a plurality of receive (Rx)antennas. The MISO system uses a plurality of Tx antennas and one Rxantenna. The SISO system uses one Tx antenna and one Rx antenna. TheSIMO system uses one Tx antenna and a plurality of Rx antennas.

The multiple antenna system can use a scheme using multiple antennas. Incase of a rank 1, the scheme may be space-time coding (STC) (e.g., spacefrequency block code (SFBC) and space time block code (STBC)), cyclicdelay diversity (CDD), frequency switched Tx diversity (FSTD), timeswitched Tx diversity (TSTD), etc. In case of a rank 2 or higher ranks,the scheme may be spatial multiplexing (SM), generalized cyclic delaydiversity (GCDD), selective virtual antenna permutation (S-NAP), etc.The SFBC is a scheme for effectively applying selectivity in a spacedomain and a frequency domain to ensure both a diversity gain and amulti-user scheduling gain in a corresponding dimension. The STBC is ascheme for applying selectivity in the space domain and a time domain.The FSTD is a scheme in which signals transmitted to multiple antennasare divided based on frequency, and the TSTD is a scheme in which thesignals transmitted to the multiple antennas are divided based on time.The SM is a scheme for transmitting different data to each antenna toimprove a transfer rate. The GCDD is a scheme for applying selectivityin the time domain and the frequency domain. The S-VAP is a scheme usinga single precoding matrix, and includes a multi-codeword (MCW) S-VAP formixing multi-codewords to antennas in spatial diversity or spatialmultiplexing and a single codeword (SCW) S-VAP using a single codeword.

FIG. 2 shows a radio frame structure.

Referring to FIG. 2, a radio frame consists of 10 subframes. Onesubframe consists of two slots. Slots included in the radio frame arenumbered with slot numbers 0 to 19. A time required to transmit onesubframe is defined as a transmission time interval (TTI). The TTI maybe a scheduling unit for data transmission. For example, one radio framemay have a length of 10 milliseconds (ms), one subframe may have alength of 1 ms, and one slot may have a length of 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of subframes included in the radio frame or the numberof slots included in the subframe may change variously.

FIG. 3 shows an example of a resource grid for one downlink slot.

Referring to FIG. 3, the downlink slot includes a plurality of OFDMsymbols in a time domain and N^(DL) resource blocks (RBs) in a frequencydomain. The number N^(DL) of resource blocks included in the downlinkslot depends on a downlink transmission bandwidth determined in a cell.For example, in an LTE system, N^(DL) may be any one of values 60 to110. One RB includes a plurality of subcarriers in the frequency domain.

Each element on the resource grid is referred to as a resource element.The resource element on the resource grid can be identified by an indexpair (k, l) within the slot. Herein, k (k=0, . . . , N^(DL)×12−1)denotes a subcarrier index in the frequency domain, and l (l=0, . . . ,6) denotes an OFDM symbol index in the time domain.

Although it is described herein that one RB includes 7×12 resourceelements consisting of 7 OFDM symbols in the time domain and 12subcarriers in the frequency domain for example, the number of OFDMsymbols and the number of subcarriers in the RB are not limited thereto.Thus, the number of OFDM symbols and the number of subcarriers maychange variously depending on a cyclic prefix (CP) length, a frequencyspacing, etc. For example, when using a normal CP, the number of OFDMsymbols is 7, and when using an extended CP, the number of OFDM symbolsis 6. In one OFDM symbol, the number of subcarriers may be selected from128, 256, 512, 1024, 1536, and 2048.

FIG. 4 shows a structure of a subframe.

Referring to FIG. 4, the subframe includes two consecutive slots. Amaximum of three OFDM symbols located in a front portion of a 1st slotwithin the subframe correspond to a control region to be assigned with aPDCCH. The remaining OFDM symbols correspond to a data region to beassigned with a PDSCH. The PDCCH informs a UE of resource assignment ofthe PCH and DL-SCH, and also informs the UE of HARQ information relatedto the DL-SCH. The PDCCH may carry an uplink (UL) scheduling grant whichinforms the UE of resource assignment for uplink transmission. Inaddition to the PDCCH, control channels such as a PCFICH, a PHICH, etc.,can be assigned to the control region. The PCFICH informs the UE of thenumber of OFDM symbols used for transmission of the PDCCHs within asubframe. The PCFICH can be transmitted in every subframe. The PHICHcarries HARQ acknowledgement (ACK)/negative-acknowledgement (NACK)signals in response to uplink transmission. The UE can read datainformation transmitted through the PDSCH by decoding controlinformation transmitted through the PDCCH. Although the control regionincludes three OFDM symbols herein, this is for exemplary purposes only.Thus, two OFDM symbols or one OFDM symbol may be included in the controlregion The number of OFDM symbols included in the control region of thesubframe can be known by using the PCFICH.

Hereinafter, a resource element used for reference signal (RS)transmission is referred to as a reference symbol. Resource elementsother than the reference symbol can be used for data transmission. Aresource element used for data transmission is referred to as a datasymbol.

The RS may be multiplied by a predetermined RS sequence whentransmitted. For example, the RS sequence may be a pseudo-random (PN)sequence, an m-sequence, etc. The RS sequence may be a binary sequenceor a complex sequence. When a BS transmits the RS multiplied by the RSsequence, a UE can reduce interference of the RS received from aneighbor cell and thus can improve channel estimation performance.

The RS can be classified into a common RS and a dedicated RS. The commonRS is an RS transmitted to all UEs in a cell. The dedicated RS is an RStransmitted to a specific UE group or a specific UE in the cell. Thecommon RS may also be referred to as a cell-specific RS. The dedicatedRS may also be referred to as a UE-specific RS. The common RS may betransmitted using all downlink subframes. The dedicated RS may betransmitted using a specific resource region allocated to the UE.

The UE may perform data demodulation and channel quality measurement byusing channel information obtained from the RS. Since a radio channelhas characteristics of delay spreading and frequency and time variationsdue to a Doppler effect, the RS has to be designed by considering afrequency and time selective channel change. Further, the RS has to bedesigned not to exceed a proper overhead so that data transmission isnot affected by the overhead caused by RS transmission.

In an LTE system having 4 Tx antennas (i.e., 4Tx transmission), an RSdefined for 4Tx is transmitted by using an SFBC-FSTD scheme for acontrol channel. A UE obtains channel information by using the RS andthen performs demodulation. In the LTE system, first 2 or 3 OFDM symbolsof a subframe consisting of 14 or 12 consecutive OFDM symbols areallocated as the control channel, and the remaining OFDM symbol of thesubframe are allocated as a data channel. In particular, the controlchannel is transmitted using a transmit diversity scheme definedaccording to an antenna configuration of the BS.

First, a common RS will be described.

FIG. 5 shows an exemplary structure of a common RS for one antenna. FIG.6 shows an exemplary structure of a common RS for two antennas. FIG. 7shows an exemplary structure of a common RS for four antennas in asubframe when using a normal CP. FIG. 8 shows an exemplary structure ofa common RS for four antennas in a subframe when using an extended CP.The section 6.10.1 of 3GPP TS 36.211 V8.4.0 (2008-09) TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Physical Channels and Modulation (Release 8) maybe incorporated herein by reference.

Referring to FIGS. 5 to 8, in case of multiple antenna transmissionusing a plurality of antennas, a resource grid exists for each antenna,and at least one RS for each antenna may be mapped to the resource grid.The RS for each antenna consists of reference symbols. Rp denotes areference symbol of an antenna #p (where pε{0, 1, 2, 3}). R0 to R3 arenot mapped to overlapping resource elements.

In one OFDM symbol, each Rp may be positioned with a spacing of 6subcarriers. In a subframe, the number of R0 s is equal to the number ofR1 s, and the number of R2 s is equal to the number of R3 s. In thesubframe, the number of R2 s and R3 s is less than the number of R0 sand R1 s. Rp is not used in any transmission through antennas except forthe antenna #p. This is to avoid inter-antenna interference. The numberof transmitted common RSs is equal to the number of antennasirrespective of the number of streams. The common RS has an independentRS for each antenna. A frequency-domain position and a time-domainposition of the common RS in the subframe are determined irrespective ofthe UEs. A common RS sequence to be multiplied by the common RS isgenerated also irrespective of the UEs. Therefore, all UEs within thecell can receive the common RS. However, a position of the common RS inthe subframe and the common RS sequence may be determined according to acell identifier (ID). Thus, the common RS is also referred to as acell-specific RS.

More specifically, the time-domain position of the common RS in thesubframe may be determined according to an antenna number and the numberof OFDM symbols in a resource block. The frequency-domain position ofthe common RS in the subframe may be determined according to an antennanumber, a cell ID, an OFDM symbol index t, a slot number in a radioframe, etc.

The common RS sequence may be used in one subframe on an OFDM symbolbasis. The common RS sequence may vary according to a cell ID, a slotnumber in one radio frame, an OFDM symbol index in a slot, a CP type,etc.

In an OFDM symbol including reference symbols, the number of referencesymbols for each antenna is 2. Since a subframe includes N^(DL) resourceblocks in the frequency domain, the number of reference symbols for eachantenna is 2×N^(DL) in one OFDM symbol. Thus, a common RS sequence has alength of 2×N^(DL).

When r(m) denotes a common RS sequence, Equation 1 shows an example of acomplex sequences used as r(m).

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2\; m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2\; m} + 1} \right)}}} \right)}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Herein, n_(s) denotes a slot number in a radio frame, and l denotes anOFDM symbol number in a slot. m is 0, 1, . . . , 2N^(max,DL)−1.N^(max,DL) denotes the number of resource blocks corresponding to amaximum bandwidth. For example, in the LTE system, N^(max,DL) may be110. c(i) denotes a PN sequence, and may be defined by a gold sequencehaving a length of 31. Equation 2 shows an example of the sequence c(i)having a length of 2×N^(max,DL).c(n)=(x ₁(n+N _(c))+x ₂(n+N _(c)))mod 2  [Equation 2]x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₁(n+1)+x ₁(n))mod 2

Herein, N_(c) is 1600, x₁(i) denotes a 1^(st) m-sequence, and x₂(i)denotes a 2^(nd) m-sequence. For example, the 1^(st) m-sequence or the2^(nd) m-sequence can be initialized according to a cell ID for eachOFDM symbol, a slot number in one radio frame, an OFDM symbol index in aslot, a CP type, etc. Equation 3 shows an example of an initialized PNsequence c_(init).c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)  [Equation 3]

Herein, N_(CP) is 1 in case of a normal CP, and is 0 in case of anextended CP.

The generated common RS sequence is mapped to a resource element.Equation 4 shows an example of mapping the common RS sequence to theresource element. The common RS sequence may be mapped to complex-valuedmodulation symbols a_(k,l) ^((P)) for an antenna p in the slot n_(s).

$\begin{matrix}{{a_{k,l}^{(p)} = {r_{l,n_{s}}\left( m^{\prime} \right)}}{k = {{6\; m} + {\left( {v + v_{shift}} \right){mod}\; 6}}}{l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\mspace{11mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {m + N_{RB}^{\max,{DL}} - N_{RB}^{DL}}}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Herein, u and u_(shift) are defined by frequency-domain positions fordifferent RSs. u may be given as shown in Equation 5.

$\begin{matrix}{v = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}{mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}{mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

A cell-specific frequency shift u_(shift) can be defined as shown inEquation 6.v _(shift)=N_(ID) ^(cell) mod 6  [Equation 6]

Meanwhile, in a system having a smaller bandwidth than N^(max,DL), onlya certain part of the RS sequence generated in a length of 2×N^(max,DL)may be selected and used.

Now, a dedicated RS will be described.

FIG. 9 shows an exemplary structure of a dedicated RS in a subframe whenusing a normal CP. FIG. 10 shows an exemplary structure of a dedicatedRS in a subframe when using an extended CP.

Referring to FIGS. 9 and 10, when using the normal CP, one TTI includes14 OFDM symbols. When using the extended CP, one TTI includes 12 OFDMsymbols. Herein, R5 denotes a reference symbol of an antenna #5transmitting the dedicated RS. When using the normal CP, the referencesymbol is positioned with a spacing of 4 subcarriers in one OFDM symbolincluding the reference symbol. When using the extended CP, thereference symbol is positioned with a spacing of 3 subcarriers in oneOFDM symbol including the reference symbol.

The number of transmitted dedicated RSs is equal to the number ofstreams. The dedicated RS may be used when a BS transmits downlinkinformation to a specific UE by performing beamforming on the downlinkinformation. The dedicated RS may be included in a data region insteadof a control region. The dedicated RS may be transmitted using aresource block to which a PDSCH is mapped. That is, a dedicated RS for aspecific UE may be transmitted through a PDSCH allocated to the specificUE.

A frequency-domain position and a time-domain position of the dedicatedRS in a subframe may be determined according to a resource blockallocated for PDSCH transmission. A dedicated RS sequence to bemultiplied by the dedicated RS may be determined according to a UE ID.In this case, only the specific UE corresponding to the UE ID in a cellmay receive the dedicated RS. Therefore, the dedicated RS is alsoreferred to as a UE-specific RS.

More specifically, the time-domain position of the dedicated RS in thesubframe may be determined according to a slot number in a radio frameand a CP type. The frequency-domain position of the dedicated RS in thesubframe may be determined according to a resource block allocated forPDSCH transmission, a cell ID, an OFDM symbol index l, a CP type, etc.

The common RS and the dedicated RS may be simultaneously used. Forexample, it is assumed that control information is transmitted on 3 OFDMsymbols (l=0, 1, 2) of a 1^(st) slot in a subframe. OFDM symbols indexedwith 0, 1, and 2 (l=0, 1, 2) may use the common RS. The remaining OFDMsymbols other than the 3 OFDM symbols may use the dedicated RS.

In the multiple antenna system in which the antenna configurationincreases, there is a need to design an RS structure and a transmissionscheme depending on the increased antenna configuration. For example, ifthe antenna configuration increases from the existing 4Tx system to an8Tx system, an RS of each antenna may be transmitted by beingmultiplexed in a time domain or a frequency domain or a code domain toidentify channels of eight Tx antennas. An RS for each antenna may be anRS for channel measurement for each Tx antenna. Hereinafter, the RS forchannel measurement for each Tx antenna is referred to as a channelquality measurement reference signal (or simply, CQI RS).

FIG. 11 shows a method of transmitting a reference signal in amulti-antenna system according to an embodiment of the presentinvention.

Referring to FIG. 11, a BS transmits a CQI RS (CRS) configurationindicator to a UE (step S101). The CRS configuration indicator mayindicate the entirety or part of radio resource information capable oftransmitting a CQI RS (or CRS), for example, a subframe in which the CQIRS is transmitted, period information, a time offset, an OFDM symbol inthe subframe and/or CRS configuration information such as a resourceelement, a resource element pattern in the subframe, antennainformation, etc.

The subframe in which the CQI RS is transmitted may be a subframe whichis not a subframe in which a primary synchronization channel (P-SCH), asecondary synchronization channel (S-SCH), or a physical-broadcastchannel (BCH) is transmitted. The P-SCH is used to acquire OFDM symbolsynchronization or slot synchronization. The P-SCH is located in a lastOFDM symbol of a slot 0 and a slot 10. That is, the P-SCH is transmittedin a subframe 0 and a subframe 5. The S-SCH is used to acquire framesynchronization. The S-SCH is located in an OFDM symbol immediatelybefore the last OFDM symbol of the slot 0 and the slot 10. That is, theS-SCH is transmitted in the subframe 0 and the subframe 5. The number ofOFDM symbols to which the P-SCH and the S-SCH are deployed on a slot orlocations thereof are for exemplary purposes only, and can changevariously depending on a system. The P-BCH is located in the subframe 0in a radio frame. The P-BCH is used to acquire basic systemconfiguration information of the BS. The P-BCH can be transmittedperiodically. For example, the P-BCH can have a period of 40 ms.

The CQI RS can be transmitted periodically, and period informationindicates a period thereof. For example, the CQI RS can be transmittedrepetitively with a period corresponding to 5, 10, 20, and 50 subframes.The time offset indicates offset information for a subframe scheduled totransmit the CQI RS. For example, a CQI RS which is scheduled to betransmitted in a subframe n can be transmitted in any one of subframesn+0, n+1, n+2, n+3, and n+4 if the time offset is given.

The antenna information indicates information on an antenna whichadditionally requires a CQI RS according to whether a cell-specific RS(i.e., a common RS) used in the conventional system is utilized as theCQI RS. For example, the common RS used in the conventional system thatuses 4 antennas can be used as a CQI RS in a new system that uses 8antennas. In this case, the number of antennas that additionally requirethe CQI RS may differ depending on the number of antennas to which thecommon RS used in the conventional system is applied among the 8antennas. If the conventional common RS is used only for one of the 8antennas, the CQI RS is necessary only for 7 antennas. Alternatively, ifthe conventional common RS is used for two or four antennas, the CQI RSis necessary for six or four antennas. Alternatively, without having touse the common RS used in the conventional system, the CQI RS can bedefined for the 8 antennas. Although an example of defining the CQI RSfor the 8 antennas will be described hereinafter, the present inventionis not limited thereto. Thus, the present invention can also apply to acase where the conventional common RS is re-utilized as the CQI RS.

The CQI RS configuration indicator that indicates any one of theaforementioned information may be broadcast to all UEs in a cell, andmay be transmitted through an L1/L2 signal to a specific UE or UE group.

The BS transmits a CQI RS (i.e., CRS) to the UE (step S102). A radioresource to which the CQI RS is deployed in a subframe, that is, an OFDMsymbol and/or a resource element in a subframe in which the CQI RS isdeployed, a resource element pattern in the subframe, or the like whenthe BS transmits the CQI RS will be described below in detail.

The UE receives the CQI RS and measures a channel for each Tx antenna(step S103). After channel measurement, the UE feeds back downlinkchannel measurement information such as a channel quality indicator(CQI) to the BS (step S104).

Now, a resource element pattern and a resource element capable ofdeploying a CQI RS in a subframe will be described.

The CQI RS can be deployed to a radio resource other than a radioresource to which a common RS or a dedicated RS is deployed. In case ofa normal CP, the common RS can be transmitted in OFDM symbols 0, 4, 7,and 11 in transmission using two antennas, and can be additionallytransmitted in OFDM symbols 1 and 8 in transmission using four antennas.The dedicated RS can be transmitted in OFDM symbols 3, 6, 9, and 12 in atime domain (this is for exemplary purposes only, and thus the dedicatedRS can also be transmitted in other OFDM symbols, and the same is truehereinafter). Therefore, the CQI RS can be deployed to any one of OFDMsymbols 5, 10, and 13 other than OFDM symbols to which the common RS andthe dedicated RS are deployed, and can be optionally deployed to theOFDM symbol 8.

In case of an extended CP, the common RS can be transmitted in OFDMsymbols 0, 3, 6, and 9 in the time domain in transmission using twoantennas, and can be additionally transmitted in OFDM symbols 1 and 7 intransmission using four antennas. The dedicated RS can be transmitted inOFDM symbols 4, 7, and 10 in the time domain. Therefore, the CQI RS canbe deployed to symbols 5, 8, and 11 other than OFDM symbols to which thecommon RS and the dedicated RS are deployed.

Unlike the aforementioned example, the location of the dedicated RS canvary depending on a system. For example, the dedicated RS can bedeployed to OFDM symbols 5, 6, 12, and 13 when using the normal CP in asystem such as an LTE-A system, and can be deployed to OFDM symbols 4,5, 10, and 11 when using the extended CP. In this case, the CQI RS canbe deployed to a radio resource other than a radio resource to which theaforementioned common RS and dedicated RS (for the LTE-A) are deployed.

The CQI RS can be transmitted by being deployed to at least one OFDMsymbol among OFDM symbols in a subframe. Among these OFDM symbol(s), theCQI RS can be deployed to 4, 6, 8, 12, or 16 resource elements. In caseof a multi-antenna system, there is a need to identify CQI RSs perantenna. This is to avoid interference between the CQI RSs per antenna.To identify the CQI RSs per antenna, frequency division multiplexing(FDM), time division multiplexing (TDM), or code division multiplexing(CDM) can be used. In the FDM, the CQI RSs per antenna are transmittedby being divided in a frequency domain. In the TDM, the CQI RSs perantenna are transmitted by being divided in a time domain. In the CDM,the CQI RSs per antenna are transmitted by using different sequences.When transmitting RSs through multiple antennas by using the FDM and theTDM, resource elements to which the CQI RS per antenna are deployed donot overlap. When using the CDM, the resource elements to which the CQIRSs per antenna are deployed may overlap.

Now, examples of deploying a CQI RS to 4, 6, or 8 resource elements inone OFDM symbol in a subframe will be sequentially described. In case ofthe normal CP, any one of OFDM symbols 5, 8, 10, and 13 can be selectedas the CQI RS. In case of the extended CP, any one of OFDM symbols 5, 8,and 11 can be selected. In addition, according to a location of adedicated RS, any one of OFDM symbols 3, 5, 6, 8, 9, 10, 12, and 13 canbe selected in case of the normal CP, and any one of OFDM symbols 4, 5,7, 8, 10, and 11 can be selected in case of the extended CP.

When the dedicated RS is deployed similarly to the LTE-A, the CQI RS canbe selected from any one of OFDM symbols 3, 8, 9, and 10 in case of thenormal CP, and can be selected from any one of OFDM symbols 2, 7, and 8in case of the extended CP.

FIG. 12 shows an example of deploying a CQI RS to four resource elementsin one OFDM symbol.

Referring to FIG. 12, the CQI RS is deployed to four resource elementsin a resource region which includes one OFDM symbol in a time domain andincludes 12 subcarriers in a frequency domain. The resource elements towhich the CQI RS is deployed can be deployed by being spaced apart fromeach other by the same distance. For example, the resource elements canbe deployed by being spaced apart from each other by a distancecorresponding to three resource elements. The CQI RS can be deployed byidentifying 8 antennas according to CDM or {CDM, TDM}.

For example, the CQI RS deployed to four resource elements can besubjected to CDM to be able to identify 8 antennas. That is, fouridentical resource elements are subjected to CDM with different codes tobe able to identify the 8 antennas. Then, the CQI RS for all of the 8antennas can be transmitted in one subframe. In this case, a duty cyclemay be 1.

Alternatively, the CQI RS can be subjected to CDM to be able to identifyfour antennas in one subframe, and can be transmitted by identifying 8antennas by the use of two subframes configured in this manner. Forexample, a CQI RS for antennas 0, 1, 2, and 3 can be transmitted byperforming CDM in a subframe n (where n is an integer), and a CQI RS forantennas 4, 5, 6, and 7 can be transmitted by performing CDM in asubframe n+k (where k is a natural number greater than or equal to 1).That is, the CQI RS can be transmitted by performing CDM and TDM. Inthis case, a duty cycle may be 2.

Alternatively, the CQI RS can be subjected to CDM to be able to identifytwo antennas in one subframe, and can be transmitted by identifying 8antennas by the use of four subframes configured in this manner. Forexample, a CQI RS for antennas 0 and 1 can be transmitted by performingCDM in a subframe n, and likewise, a CQI RS for antennas 2 and 3, a CQIRS for antennas 4 and 5, and a CQI RS for antennas 6 and 7 can betransmitted by performing CDM respectively in subframes n+1, n+2, andn+3. In this case, a duty cycle may be 4. Although consecutive subframesare shown for example in the example above, the present invention is notlimited thereto.

Alternatively, a CQI RS for one antenna can be transmitted in onesubframe such that the CQI RS is transmitted by identifying 8 antennasby the use of 8 subframes. In this case, a duty cycle may be 8.

If it is assumed that OFDM symbols of the subframe are indexed from 0 to13 (in case of a normal CP), an OFDM symbol to which the CQI RS can bedeployed in the subframe may be any one of OFDM symbols 5, 8, 10, and 13in case of the normal CP. In case of an extended CP, the OFDM symbol maybe any one of OFDM symbols 5, 8, and 11. If a dedicated RS is deployedsimilarly to LTE-A, a CQI RS may be selected from any one of OFDMsymbols 3, 8, 9, and 10 in case of the normal CP, and may be selectedfrom any one of OFDM symbols 2, 7, and 8 in case of the extended CP.That is, the CQI RS can be deployed to an OFDM symbol other than OFDMsymbols to which a common RS and a dedicated RS are deployed in thesubframe. According to which OFDM symbol the dedicated RS is deployed,an OFDM symbol to which the CQI RS can be deployed can change variously.

Although a case of identifying a CQI RS with respect to 8 antennas isexemplified in the above example, the present invention is not limitedthereto. The conventionally defined legacy RS can apply to at least oneof a plurality of antennas, and the CQI RS according to the presentinvention can apply to the remaining antennas. For example, amongantennas 0 to 8, the legacy RS can be used for the antenna 0, and theCQI RS according to the present invention can be used for antennas 1 to7.

The CQI RS can be applied in such a manner that a position of a resourceelement in an OFDM symbol per cell is shifted. Alternatively, thelocation of the resource element in which the CQI RS is deployed may befixed in all cells.

FIG. 13 shows examples of deploying two CQI RSs to four resourceelements in one OFDM symbol.

Unlike FIG. 12, two CQI RSs are deployed to four resource elements inFIG. 13. That is, a CQI RS 1 can be deployed to two resource elements,and a CQI RS 2 can be deployed to the remaining two resource elements.The CQI RS can be deployed to the resource elements in such a patternthat the resource elements are spaced apart from each other by the sameresource element distance as shown in FIG. 13 (a), and in such a patternthat the CQI RS is deployed to two consecutive resource element pairsand the resource element pairs are spaced apart from each other by aspecific resource element distance as shown in FIG. 13 (b).Alternatively, as shown in FIG. 13 (c), a resource element to which theCQI RS 1 is deployed and a resource element to which the CQI RS 2 isdeployed may have a different resource element distance. The CQI RS 1and the CQI RS 2 can be identified by using different basic sequences.

The CQI RS 1 and the CQI RS 2 can be deployed by identifying 8 antennasby the use of {CDM, FDM} or {CDM, FDM, TDM} or {FDM, TDM}.

In case of using {CDM, FDM}, the CQI RS 1 deployed to two resourceelements among four resource elements can be subjected to CDM to be ableto identify four antennas (e.g., antennas 0 to 3), and the CQI RS 2deployed to the remaining two resource elements can also be subjected toCDM to be able to identify four antennas (i.e., antennas 4 to 7). Then,the CQI RS for all of 8 antennas can be transmitted in one subframe.

In case of using {CDM, FDM, TDM}, the CQI RS can be subjected to {CDM,FDM} to be able to identify four antennas in one subframe, and can betransmitted by identifying 8 antennas by the use of two subframesconfigured in this manner. For example, the CQI RS 1 can be subjected toCDM to be able to identify antennas 0 and 1 in a subframe n (where n isan integer), and the CQI RS 2 can be subjected to CDM to be able toidentify antennas 2 and 3. As described above, the CQI RS 1 and the CQIRS 2 are subjected to FDM since they are allocated to different resourceelements. In a subframe n+k (where k is a natural number greater than orequal to 1), the CQI RS 1 is subjected to CDM to be able to identifyantennas 4 and 5, and the CQI RS 2 can be subjected to CDM to be able toidentify antennas 6 and 7. In this case, a duty cycle may be 2.

In case of using {FDM, TDM}, the CQI RS 1 and the CQI RS 2 can identifytwo antennas in one subframe, and can be transmitted by identifying 8antennas by the use of four subframes configured in this manner. Forexample, the CQI RS 1 and the CQI RS 2 can be used respectively for anantenna 0 and an antenna 1 in a subframe n, for an antenna 2 and anantenna 3 in a subframe n+1, for an antenna 4 and an antenna 5 in asubframe n+2, and for an antenna 6 and an antenna 7 in a subframe n+3.In this case, a duty cycle may be 4. Although consecutive subframes areexampled in the above example, the present invention is not limitedthereto.

FIG. 14 shows examples of deploying four CQI RSs to four resourceelements in one OFDM symbol.

Unlike FIG. 13, four CQI RSs are deployed to four resource elements inFIG. 14. That is, a CQI RS 1 to a CQI RS 4 are deployed one by one toevery one resource element among the four resource elements. The CQI RScan be deployed to the resource elements in such a pattern that theresource elements are spaced apart from each other by the same resourceelement distance as shown in FIG. 14 (a) and FIG. 14 (c) (i.e., adistance of 3 resource elements in FIG. 14 (a) and a distance of 2resource elements in FIG. 14( c)), and the CQI RS 1 to the CQI RS 4 canbe deployed to four consecutive resource elements as shown in FIG. 14(b). The CQI RS 1 to the CQI RS 4 can be identified by using differentbasic sequences.

The CQI RS 1 to the CQI RS 4 can be deployed by identifying 8 antennasby the use of {CDM, FDM} or {FDM, TDM}.

In case of using {CDM, FDM}, each of the CQI RS 1 to the CQI RS 4 can besubjected to CDM to be able to identify 8 antennas by identifying twoantennas in one subframe.

In case of using {FDM, TDM}, 8 antennas can be identified in such amanner that the CQI RS 1 to the CQI RS 4, which are identified by FDM,identify four antennas (e.g., antennas 0 to 3) in one subframe and theCQI RS 1 to the CQI RS 4, which are identified by FDM, identify fourantennas (i.e., antennas 4 to 7) in another subframe.

FIG. 15 shows an example of applying a CQI RS deployment methoddescribed in FIG. 14 to a subframe.

Referring to FIG. 15, in case of a normal CP, CQI RSs 1 to 4 aredeployed to an OFDM symbol 13 of a second slot. In case of an extendedCP, the CQI RS 1 to the CQI RS 4 are deployed to an OFDM symbol 11 ofthe second slot. That is, this is an example of applying a resourceelement pattern in which the CQI RS is deployed as described in FIG. 14(a). Although not shown in FIG. 15, the same can also apply to theresource element pattern of FIG. 14 (b) and FIG. 14 (c). In addition,although an example of applying the CQI RS 1 to the CQI RS 4 to a lastOFDM symbol of a subframe is described in FIG. 15, it is apparent thatthe present invention is also applicable to any one of OFDM symbolsexcept for an OFDM symbol to which a common RS (or cell specific RS) ora dedicated RS are deployed.

FIG. 16 shows examples of deploying a CQI RS to 6 resource elements inone OFDM symbol.

Referring to FIG. 16 (a), the CQI RS is deployed to the 6 resourceelements in a resource region including one OFDM symbol in a time domainand 12 subcarriers in a frequency domain. The resource element to whichthe CQI RS is deployed can be deployed by being spaced apart from eachother by the same resource element distance (i.e., a distance of tworesource elements). The CQI RS can be deployed by identifying 8 antennasby the use of CDM or {CDM, TDM} or {FDM, TDM}.

For example, the CQI RS deployed to the 6 resource elements in onesubframe can be subjected to CDM to be able to identify 8 antennas.Alternatively, the CQI RS can be subjected to CDM to be able to identify4 antennas in one subframe, and can be transmitted by identifying 8antennas by the use of 2 subframes configured in this manner. Forexample, a CQI RS for antennas 0, 1, 2, and 3 can be transmitted byperforming CDM in a subframe n (where n is an integer), and a CQI RS forantennas 4, 5, 6, and 7 can be transmitted by performing CDM in asubframe n+k (where k is a natural number greater than or equal to 1).That is, the CQI RS can be transmitted by performing CDM and TDM.

In case of FIG. 16 (a), a position at which the CQI RS can be deployedcan be shifted for each cell. For example, a position of a resourceelement to which a CQI RS is deployed can be determined by a modular-2operation. In case of FIG. 16 (b) to FIG. 16 (g), a position of aresource element to which a CQI RS is deployed for each cell can befixed to the same position, and can change depending on offsetinformation. The offset information may provide a offset value in a unitof resource elements with respect to a start position which is used as areference point, and may indicate the start position by using an index.For example, if FIG. 16 (b) shows the start position used as thereference position, the offset value may be set to 1 in FIG. 16 (c), 2in FIG. 16 (d), and 3 in FIG. 16 (e). The offset value can be set to adifferent value in a unit of cell or cell group to the offset value.Alternatively, a position of a resource element to which a CQI RS isdeployed can be determined by a modular-6 operation.

FIG. 17 shows an example of applying a CQI RS deployment methoddescribed in FIG. 16. In this example, the CQI RS deployment methoddescribed in FIG. 16 (a) is applied to a last OFDM symbol. Unlike FIG.17, if a dedicated RS is deployed similarly to LTE-A, any one of OFDMsymbols 3, 8, 9, and 10 can be selected as the CQI RS in case of anormal CP, and any one of OFDM symbols 2, 7, and 8 can be selected asthe CQI RS in case of an extended CP.

Now, examples in which a CQI RS is transmitted in one OFDM symbol in asubframe and in which a CQI RS is deployed to 8 resource elements in afrequency band corresponding to one resource block will be described.

FIG. 18 shows an example in which a CQI RS is transmitted in one OFDMsymbol in a subframe and in which a CQI RS is deployed to 8 resourceelement in a frequency band corresponding to one resource block.

Referring to FIG. 18, a CQI RS 1 is deployed to 8 resource elements in aresource region including one OFDM symbol in a time domain and 12subcarriers in a frequency domain. Each of resource elements to whichthe CQI RS 1 is deployed can be deployed in pair, and can be deployed bybeing spaced apart by the same distance. Herein, the CQI RS 1 may be aCQI RS that uses one basic sequence. The CQI RS 1 can be deployed byidentifying 8 antennas by the use of CDM or {CDM,TDM}.

For example, 8 resource elements to which the CQI RS 1 is deployed canbe subjected to CDM to be able to identify 8 antennas. That is, 8identical resource elements are subjected to CDM with different codes tobe able to identify the 8 antennas. In this case, the CQI RS for all ofthe 8 antennas can be transmitted in one subframe. A duty cycle may beone subframe.

Alternatively, the CQI RS 1 can be subjected to CDM to be able toidentify 4 antennas in 8 resource elements in one subframe, and can betransmitted by identifying 8 antennas by the use of 2 subframesconfigured in this manner. For example, a CQI RS for antennas 0, 1, 2,and 3 can be transmitted by performing CDM in a subframe n, and a CQI RSfor antennas 4, 5, 6, and 7 can be transmitted by performing CDM in asubframe n+1. That is, the CQI RS can be transmitted by performing CDMand TDM. In this case, a duty cycle may be two subframes.

Alternatively, the CQI RS 1 can be subjected to CDM to be able toidentify two antennas in 8 resource elements in one subframe, and can betransmitted by identifying 8 antennas by the use of two subframesconfigured in this manner. For example, a CQI RS for antennas 0 and 1can be transmitted by performing CDM in a subframe n, and likewise, aCQI RS for antennas 2 and 3, a CQI RS for antennas 4 and 5, and a CQI RSfor antennas 6 and 7 can be transmitted by performing CDM respectivelyin subframes n+1, n+2, and n+3. In this case, a duty cycle may be 4subframes.

Alternatively, the CQI RS 1 for one antenna can be transmitted in 8resource elements in one subframe such that it is transmitted byidentifying 8 antennas by the use of the 8 subframes. In this case, aduty cycle may be 8 subframes.

If it is assumed that OFDM symbols of the subframe are indexed from 0 to13 (in case of a normal CP), an OFDM symbol to which the CQI RS 1 can bedeployed in the subframe may be any one of OFDM symbols 5, 8, 10, and 13in case of the normal CP. In case of an extended CP, the OFDM symbol maybe any one of OFDM symbols 5, 8, and 11. If a dedicated RS is deployedsimilarly to LTE-A, a CQI RS may be selected from any one of OFDMsymbols 3, 8, 9, and 10 in case of the normal CP, and may be selectedfrom any one of OFDM symbols 2, 7, and 8 in case of the extended CP.That is, the CQI RS can be deployed to an OFDM symbol to which a commonRS and a dedicated RS are not deployed in the subframe. In addition,according to a position at which the dedicated RS is deployed, an OFDMsymbol to which the CQI RS 1 can be deployed can change variously.

FIG. 19 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which a CQI RS is deployed to 8resource element in a frequency band corresponding to one resourceblock.

Referring to FIGS. 19 (a) to 19 (e), the CQI RS can be deployed to 8consecutive resource elements in a frequency domain. A start position ofresource elements to which the CQI RS is deployed can be fixed, and canchange depending on offset information. The offset information mayprovide a offset value in a unit of resource elements with respect to astart position which is used as a reference point, and may indicate thestart position by using an index. For example, if FIG. 19 (a) shows thestart position used as the reference position, the offset value may beset to 1 in FIG. 19( b), 2 in FIG. 19( c), 3 in FIG. 19( d), and 4 inFIG. 19( e). The offset value may be set to a different value in a unitof cell or cell group to the offset value.

FIG. 20 shows an example in which a CQI RS is transmitted in one OFDMsymbol in a subframe and in which two CQI RSs are deployed to 8 resourceelements in a frequency band corresponding to one resource block.

Referring to FIG. 20, a CQI RS 1 is deployed to four resource elements,and a CQI RS 2 is deployed to another four resource elements. The CQI RS1 and the CQI RS 2 can use different basic sequences. The CQI RS 1 andthe CQI RS 2 can be deployed by identifying 8 antennas by the use of{CDM and FDM} or {CDM, FDM, and TDM}.

For example, four resource elements to which the CQI RS 1 is deployedcan be subjected to CDM to be able to identify four antennas (e.g.,antennas 0, 1, 2, and 3), and four resource elements to which the CQI RS2 is deployed can be subjected to CDM to be able to identify fourantennas (e.g., antennas 4, 5, 6, and 7). That is, the CQI RS 1 and theCQI RS 2 can be subjected to FDM, and the CQI RS 1 and the CQI RS 2 canbe subjected to CDM. In this case, a CQI RS for all 8 antennas can betransmitted in one subframe. A duty cycle may be one subframe.

Alternatively, the CQI RS 1 can be subjected to CDM to be able toidentify two antennas (e.g., antennas 0 and 1) in four resource elementsin one subframe, and the CQI RS 2 can be subjected to CDM to be able toidentify two antennas (e.g., antennas 2 and 3) in another four resourceelements in the same subframe. The CQI RS can be transmitted byidentifying 8 antennas by the use of two subframes configured in thismanner. For example, in a subframe n, the CQI RS 1 is transmitted byperforming CDM for antennas 0 and 1 and the CQI RS 2 is transmitted byperforming CDM for antennas 2 and 3. In addition, in a subframe n+1, theCQI RS 1 can be transmitted by performing CDM for antennas 4 and 5, andcan be transmitted by performing CDM for antennas 6 and 7. That is, theCQI RS can be transmitted by performing CDM, TDM, and FDM. In this case,a duty cycle may be two subframes.

Alternatively, the CQI RS 1 can be deployed to be able to identify oneantenna in four resource elements in one subframe, and the CQI RS 2 canbe deployed to identify another antenna in another four resourceelements in the same subframe. The CQI RS can be transmitted byidentifying 8 antennas by the use of four subframes configured in thismanner. For example, in a subframe n, the CQI RS 1 and the CRI RS 2 canbe transmitted by performing FDM for an antenna 0 and an antenna 1,respectively. In a subframe n+1, the CQI RS 1 and the CQI RS 2 can betransmitted by performing FDM for an antenna 2 and an antenna 3,respectively. In a subframe n+2, the CQI RS 1 and the CQI RS 2 can betransmitted by performing FDM for an antenna 4 and an antenna 5,respectively. In a subframe n+3, the CQI RS 1 and the CQI RS 2 can betransmitted by performing FDM for an antenna 6 and an antenna 7,respectively. In this case, a duty cycle may be 4 subframes.

FIG. 21 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which two CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

Referring to FIG. 21 (a), the 8 resource elements are consecutiverepetitively in the order of a resource element to which a CQI RS 2 isdeployed and a resource element to which a CQI RS 1 is deployed.Referring to FIG. 21 (b), there are four consecutive resource elementsto which a CQI RS 2 is deployed, and subsequently, there are fourconsecutive resource elements to which a CQI RS 1 is deployed. A startposition of resource elements to which the CQI RS is deployed can befixed, and can change depending on offset information. The offsetinformation may provide a offset value in a unit of resource elementswith respect to a start position which is used as a reference point, andmay indicate the start position by using an index. Although not shown,the offset value may be set to any one of values 1 to 4. The offsetvalue may be determined in a unit of cell or cell group.

FIG. 22 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which four CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

Referring to FIG. 22, each of a CQI RS 1 to a CQI RS 4 is deployed totwo resource elements in a resource region including one OFDM symbol ina time domain and 12 subcarriers in a frequency domain. The CQI RS 1 tothe CQI RS 4 can use different basic sequences. The CQI RS 1 to the CQIRS 4 can be deployed by identifying 8 antennas by the use of {CDM andFDM} or {FDM and TDM}.

For example, two resource elements to which the CQI RS 1 is deployed canbe subjected to CDM to be able to identify two antennas (e.g., antennas0 and 1), and two resource elements to which the CQI RS 2 is deployedcan be subjected to CDM to be able to identify two antennas (e.g.,antennas 3 and 4). Likewise, each of the CQI RS 3 and the CQI RS 4 canalso be subjected to CDM to be able to identify two antennas. That is,the CQI RS 1 to the CQI RS 4 can be subjected to FDM, and each of theCQI RS 1 to the CQI RS 4 can be subjected to CDM. In this case, the CQIRS for all of the 8 antennas can be transmitted in one subframe. A dutycycle may be one subframe.

Alternatively, each of the CQI RS 1 to the CQI RS 4 is subjected to FDMso that the CQI RSs can be transmitted for one antenna in two resourcesin one subframe, and can be transmitted by identifying the 8 antennas bythe use of two subframes configured in this manner. For example, in asubframe n, the CQI RS 1 to the CQI RS 4 can be subjected to FDM so thatthe CQI RSs are identified for antennas 0 to 3, respectively. In asubframe n+1, the CQI RS 1 to the CQI RS 4 can be subjected to FDM sothat the CQI RSs can be identified for antennas 4 to 7, respectively.That is, the CQI RSs can be transmitted by performing FDM and TDM. Inthis case, a duty cycle may be two subframes.

FIG. 23 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which four CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

Referring to FIG. 23 (a), four resource elements to which any one of aCQI RS 1 to a CQI RS 4 is deployed are deployed twice consecutively.Referring to FIG. 23 (b), a start position at which the CQI RS isdeployed is different from FIG. 23 (a). A start position of resourceelements to which the CQI RS is deployed can be fixed, and can changedepending on offset information. The offset information may provide aoffset value in a unit of resource elements with respect to a startposition which is used as a reference point, and may indicate the startposition by using an index. Although it is shown herein that the offsetvalue is 1 as illustrated in FIG. 23 (b), the offset value may be set toany one of values 1 to 4. The offset value may be determined in a unitof cell or cell group. Referring to FIG. 23 (c), four resource elementsto which any one of a CQI RS 1 to a CQI RS 4 is deployed areconsecutively deployed, whereas four resource elements to which the CQIRS is deployed are deployed by being spaced apart from each other. FIG.23 (c) shows an example in which four resource elements to which a CQIRS is deployed are deployed by being spaced apart from each other by adistance of two resource elements. Alternatively, it can also beexpressed that resource elements to which each CQI RS is deployed aredeployed by being spaced apart from each other by a distance of 6resource elements. FIG. 23 (d) shows a different start position of aresource element to which a CQI RS is deployed in comparison with FIG.23 (c).

FIG. 24 shows another example in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which 8 CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

Referring to FIG. 24, each of a CQI RS 1 to a CQI RS 7 is deployed toone resource element in a resource region including one OFDM symbol in atime domain and 12 subcarriers in a frequency domain. The CQI RS 1 tothe CQI RS 7 can use different basic sequences. The CQI RS 1 to the CQIRS 7 can be deployed by identifying 8 antennas by the use of FDM. CQIRSs for two antennas are deployed to consecutive resource elements.Consecutive two resource elements are deployed by being spaced apartfrom each other by a distance of one resource element.

FIG. 25 shows other examples in which a CQI RS is transmitted in oneOFDM symbol in a subframe and in which 8 CQI RSs are deployed to 8resource elements in a frequency band corresponding to one resourceblock.

FIG. 25 (a) and FIG. 25 (b) show a case in which there are consecutiveresource elements to which any one of a CQI RS 1 to a CQI RS 7 isdeployed for example. FIG. 25 (b) shows an example in which a startposition of a resource element to which a CQI RS is shifted by an offsetvalue 1 in comparison with FIG. 25 (a). Although it is shown herein thatthe offset value is 1 as illustrated in FIG. 25 (b), the offset valuemay be set to any one of values 1 to 4. Alternatively, as shown in FIG.25 (c) and FIG. 25 (d), four resource elements allocated for four CQIRSs are consecutive, and the two resource elements can be deployed bybeing spaced apart from each other.

FIG. 26 shows an example of applying a CQI RS deployment methoddescribed in FIG. 22 to a subframe.

Referring to FIG. 26, a CQI RS can be transmitted in a last OFDM symbolof the subframe, that is, in an OFDM symbol 13 in case of a normal CPand in an OFDM symbol 11 in case of an extended CP. Four CQI RSs (i.e.,a CQI RS 1 to a CQI RS 4) can be transmitted by performing FDM in thelast OFDM symbol of the subframe.

FIG. 27 shows an example of applying a CQI RS deployment methoddescribed in FIG. 24 to a subframe.

Referring to FIG. 27, a CQI RS can be transmitted in a last OFDM symbolof the subframe, that is, in an OFDM symbol 13 in case of a normal CPand in an OFDM symbol 11 in case of an extended CP. 8 CQI RSs (i.e., aCQI RS 1 to a CQI RS 8) can be transmitted by performing FDM in the lastOFDM symbol of the subframe.

FIG. 28 to FIG. 33 show examples of deploying 8 CQI RSs to 8 resourceelements in a subframe.

Referring to FIG. 28 to FIG. 33, a dedicated RS can be transmitted inOFDM symbols 5, 6, 12, and 13 in case of a normal CP, and can betransmitted in OFDM symbols 4, 5, 10, and 11 in case of an extended CP.In addition, a common RS can be transmitted in OFDM symbols 0, 4, 7, and11 in case of the normal CP, and can be transmitted in OFDM symbols 0,3, 6, and 9 in case of the extended CP. In this case, a CQI RS can betransmitted in any one of OFDM symbols 3, 8, 9, and 10 in case of thenormal CP, and can be transmitted in any one of OFDM symbols 7 and 8 incase of the extended CP.

FIG. 28 and FIG. 30 show a case where a CQI RS is transmitted in an OFDMsymbol 10 in case of a normal CP and in an OFDM symbol 8 in case of anextended CP for example. FIG. 28 and FIG. 29 are common in a sense thata CQI RS 1 to a CQI RS 8 have the same pattern in an OFDM symbol towhich the CQI RS is transmitted (i.e., a pattern in which there are twoconsecutive resource elements to which the CQI RS is deployed, and thetwo resource elements are spaced apart from each other by a distance ofone resource element), but are different from each other in a sense thata start position of a resource element to which the CQI RS is deployedis different.

FIG. 30 to FIG. 33 are common in a sense that a CQI RS 1 to a CQI RS 8have the same pattern in an OFDM symbol to which the CQI RS istransmitted (i.e., a pattern in which there are eight consecutiveresource elements to which the CQI RS is deployed), but are differentfrom each other in a sense that an OFDM symbol to which the CQI RS istransmitted is different. That is, FIG. 30 shows a case where a CQI RSis transmitted in an OFDM symbol 10 in case of a normal CP, and istransmitted in an OFDM symbol 8 in case of an extended CP for example.FIG. 31 shows a case where a CQI RS is transmitted in an OFDM symbol 9in case of the normal CP, and is transmitted in an OFDM symbol 8 in caseof the extended CP for example. FIG. 32 shows a case where a CQI istransmitted in an OFDM symbol 8 in case of the normal CP, and istransmitted in an OFDM symbol 7 in case of the extended CP for example.FIG. 33 shows a case where a CQI is transmitted in an OFDM symbol 3 incase of the normal CP, and is transmitted in an OFDM symbol 2 in case ofthe extended CP for example. In FIG. 28 to FIG. 33, a CQI RS 1 to a CQIRS 8 can be transmitted by performing FDM in an OFDM symbol to which theCQI RS is transmitted.

An example of deploying a CQI RS to 4, 6, or 8 resource elements in oneOFDM symbol in a subframe is described above. Now, an example ofdeploying a CQI RS to 4, 8, 12, or 16 resource elements in two OFDMsymbols in a subframe will be described.

For the CQI RS, two OFDM symbols can be selected from OFDM symbols 5, 8,10, and 13 in case of the normal CP. If the selected two OFDM symbolsare expressed such as an OFDM symbol index pair (x,y), then it can beany one of (5, 8), (5, 10), (5, 13), (8, 10), (8, 13), and (10, 13). Incase of the extended CP, two OFDM symbols can be selected from OFDMsymbols 5, 8, and 11, and it can be any one of (5, 8), (5, 11), and (8,11). In addition, according to a position of a dedicated RS, any twoOFDM symbols can be selected from OFDM symbols 3, 5, 6, 8, 9, 10, 12,and 13 in case of the normal CP, and any two OFDM symbols can beselected from OFDM symbols 4, 5, 7, 8, 10, and 11 in case of theextended CP. If the dedicated RS is deployed similarly to LTE-A, for aCQI RS, any two OFDM symbols can be selected from OFDM symbols 3, 8, 9,and 10 in case of the normal CP, and any two OFDM symbols can beselected from OFDM symbols 2, 7, and 8 in case of the extended CP.

FIG. 34 shows examples in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which a CQI RS is deployed to four resourceelements in a frequency band corresponding to one resource block.

A CQI RS is deployed to four resource elements in a resource regionincluding two OFDM symbols in a time domain (herein, each OFDM symbolmay be included in different resource blocks) and 12 subcarriers in afrequency domain. As shown in FIG. 34 (a), (b), or (d), resourceelements to which the CQI RS is deployed can be deployed by being spacedapart from each other by the same resource element distance. Forexample, the resource elements can be deployed by being spaced apartfrom each other by a distance of 6 resource elements. Alternatively, aresource element to which a CQI RS is deployed as shown in FIG. 34 (c)can be deployed to two consecutive resource elements in one OFDM symbol.

The CQI RS can be deployed by identifying 8 antennas by the use of CDMor {CDM, TDM}. For example, the CQI RS deployed to four resourceelements can be subjected to CDM to be able to identify 8 antennas.Then, the CQI RS for all of the 8 antennas can be transmitted in onesubframe. In this case, a duty cycle may be 1.

Alternatively, the CQI RS can be subjected to CDM to be able to identifyfour antennas in one subframe, and can be transmitted by identifying 8antennas by the use of two subframes configured in this manner. Forexample, a CQI RS for antennas 0, 1, 2, and 3 can be transmitted byperforming CDM in a subframe n (where n is an integer), and a CQI RS forantennas 4, 5, 6, and 7 can be transmitted by performing CDM in asubframe n+k (where k is a natural number greater than or equal to 1).That is, the CQI RS can be transmitted by performing CDM and TDM. Inthis case, a duty cycle may be 2.

Alternatively, the CQI RS can be subjected to CDM to be able to identifytwo antennas in one subframe, and can be transmitted by identifying 8antennas by the use of four subframes configured in this manner. Forexample, a CQI RS for antennas 0 and 1 can be transmitted by performingCDM in a subframe n, and likewise, a CQI RS for antennas 2 and 3, a CQIRS for antennas 4 and 5, and a CQI RS for antennas 6 and 7 can betransmitted by performing CDM respectively in subframes n+1, n+2, andn+3. In this case, a duty cycle may be 4. Although consecutive subframesare shown in the example above, the present invention is not limitedthereto. A position at which the CQI RS can be deployed for each cellcan be shifted. For example, a start position of a resource element towhich the CQI RS is deployed can be determined by a modular-3 or 6operation. Alternatively, it can be deployed to a resource element ofthe same frequency domain as a common RS.

FIG. 35 shows examples of deploying two CQI RSs to four resourceelements in two OFDM symbols.

Unlike FIG. 34, two CQI RSs are deployed to four resource elements inFIG. 35. That is, a CQI RS 1 can be deployed to two resource elementsincluded in one OFDM symbol, and a CQI RS 2 can be deployed to tworesource elements included in the remaining OFDM symbol. The CQI RSs maybe deployed to the resource elements in such a pattern that the resourceelements are spaced apart from each other by the same resource elementdistance as shown in FIGS. 35 (a), (b), and (d), and in such a patternthat the CQI RSs are deployed to two consecutive resource elements asshown in FIG. 35 (c). FIG. 35 (d) is different from FIGS. 35 (a) and (b)in a sense that the CQI RS 1 and the CQI RS 2 are deployed to sameresource elements of the frequency domain.

The CQI RS 1 and the CQI RS 2 can be deployed by identifying 8 antennasby the use of {CDM, TDM}.

In case of using {CDM, TDM}, the CQI RS 1 can be subjected to CDM to beable to identify four antennas (e.g., antennas 0 to 3), and the CQI RS 2can also be subjected to CDM to be able to identify four antennas (i.e.,antennas 4 to 7). Then, the CQI RS for all of 8 antennas can betransmitted in one subframe. In this case, a duty cycle may be 1.

Each of the CQI RS 1 and the CQI RS 2 can be subjected to CDM to be ableto identify two antennas in one subframe, and can be transmitted byidentifying 8 antennas by the use of two subframes configured in thismanner. For example, the CQI RS 1 can be subjected to CDM to be able toidentify antennas 0 and 1 in a subframe n (where n is an integer), andthe CQI RS 2 can be subjected to CDM to be able to identify antennas 2and 3. In a subframe n+k (where k is a natural number greater than orequal to 1), the CQI RS 1 is subjected to CDM to be able to identifyantennas 4 and 5, and the CQI RS 2 can be subjected to CDM to be able toidentify antennas 6 and 7. In this case, a duty cycle may be 2.

Alternatively, each of the CQI RS 1 and the CQI RS 2 can identify oneseparate antenna in one subframe, and can be transmitted by identifying8 antennas by the use of four subframes configured in this manner. Forexample, the CQI RS 1 and the CQI RS 2 can be used respectively for anantenna 0 and an antenna 1 in a subframe n, for an antenna 2 and anantenna 3 in a subframe n+1, for an antenna 4 and an antenna 5 in asubframe n+2, and for an antenna 6 and an antenna 7 in a subframe n+3.In this case, a duty cycle may be 4. Although consecutive subframes areexampled in the above example, the present invention is not limitedthereto.

FIG. 36 shows examples of deploying four CQI RSs to four resourceelements in two OFDM symbols.

Four CQI RSs are deployed to four resource elements in FIG. 36. That is,a CQI RS 1 to a CQI RS 4 are deployed one by one to every one resourceelement among the four resource elements. The CQI RS 1 to the CQI RS 4can be deployed by identifying 8 antennas by the use of {CDM, FDM, TDM}.

For example, each of the CQI RS 1 to the CQI RS 4 can be subjected toCDM in one subframe to be able to identify 8 antennas by identifying twoantennas (duty cycle 1). Alternatively, 8 antennas can be identified(duty cycle 2) in such a manner that the CQI RS 1 to the CQI RS 4, whichare identified by FDM, identify four antennas (e.g., antennas 0 to 3) inone subframe and identify another four antennas (i.e., antennas 4 to 7)in another subframe.

FIG. 37 shows an example of deploying four CQI RSs to four resourceelements in two OFDM symbols in a subframe.

A CQI RS can be deployed to each of two consecutive resource elements inone OFDM symbol as shown in FIGS. 37 (a) and (b). A CQI RS can bedeployed to resource elements spaced apart from each other as shown inFIGS. 37 (c) and (d).

FIG. 38 shows an example in which a CQI RS is deployed to four resourceelements in two OFDM symbols in a subframe wherein the resource elementsto which the CQI RS is deployed to each OFDM symbol has the samepattern.

CDM can be used to allow a CQI RS deployed to four resource elements tobe able to identify 8 antennas. Alternatively, {CDM, TDM} can be usedsuch that antennas 0 to 3 can be identified in any one of two OFDMsymbols, and antennas 4 to 7 can be identified in any one of theremaining OFDM symbol. Alternatively, the antennas 0 to 3 can beidentified by using a CQI RS deployed to two OFDM symbols in a subframen, and the antennas 4 to 7 can be identified by using a CQI RS deployedto two OFDM symbols in a subframe n+k.

FIG. 39 shows an example in which two CQI RSs are deployed to fourresource elements in two OFDM symbols in a subframe

Referring to FIG. 39, a CQI RS 1 is deployed to two resource elements inone OFDM symbol, and a CQI RS 2 is deployed to two resource elements inanother OFDM symbol. The CQI RS 1 and the CQI RS 2 can use differentbasic sequences. The CQI RS 1 and the CQI RS 2 can be deployed byidentifying 8 antennas by the use of TDM or {CDM, TDM}.

In case of TDM, each of the CQI RS 1 and the CQI RS 2 can identify oneantenna in one subframe (i.e., two antennas in total), and can identify8 antennas by using four subframes configured in this manner. In case of{CDM, TDM}, in one subframe, CDM can be performed such that the CQI RS 1identifies antennas 0 and 1 and the CQI RS 2 identifies antennas 2 and3, and in another subframe configured in a similar manner, CDM can beperformed such that the CQI RS 1 identifies antennas 4 and 5 and the CQIRS 2 identifies antennas 6 and 7 (duty cycle 2). Alternatively, CDM canbe performed such that the CQI RS 1 identifies antennas 0 to 3 and theCQI RS 2 identifies antennas 4 to 7 in one subframe (duty cycle 1). Inorder to avoid interference between CQI RSs in neighbor cells, a startposition at which the CQI RS is deployed can be shifted for each cell.In this case, a start position at which the CQI RS is deployed (i.e., aposition of a resource element) can be determined by a modular-3 or 6operation.

FIG. 40 shows examples for deploying four CQI RSs to four resourceelements in two OFDM symbols in a subframe.

If each CQI RS is used only for one antenna in one subframe, fourantennas can be identified. Therefore, a CQI RS for 8 antennas can beprovided by using two subframes (duty cycle 2). Alternatively, if eachCQI RS is used for two antennas by performing CDM in one subframe, allof the 8 antennas can be identified in one subframe (duty cycle 1).

FIG. 41 shows an example in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which a CQI RS is deployed to 8 resourceelements in a frequency band corresponding to one resource block.

Referring to FIG. 41, a CQI RS 1 is deployed to 8 resource elements in aresource region including two OFDM symbols in a time domain and 12subcarriers in a frequency domain. Each resource element to which theCQI RS 1 is deployed can be deployed by being spaced apart from eachother by the same distance, for example, a distance of 3 resourceelements.

The CQI RS 1 can be deployed by identifying 8 antennas by the use of CDMor {CDM and TDM}. For example, 8 resource elements to which the CQI RS 1is deployed can identify 8 antennas by performing CDM. That is, 8identical resource elements are subjected to CDM with different codes tobe able to identify the 8 antennas. In this case, the CQI RS for all ofthe 8 antennas can be transmitted in one subframe (duty cycle 1).

Alternatively, the CQI RS 1 can be subjected to CDM to be able toidentify four antennas in 8 resource elements in one subframe, and canbe transmitted by identifying 8 antennas by the use of two subframesconfigured in this manner. For example, a CQI RS for antennas 0, 1, 2,and 3 can be transmitted by performing CDM in a subframe n, and a CQI RSfor antennas 4, 5, 6, and 7 can be transmitted by performing CDM in asubframe n+1. That is, the CQI RS can be transmitted by performing CDMand TDM (duty cycle 2).

Alternatively, the CQI RS 1 can be subjected to CDM to be able toidentify two antennas in 8 resource elements in one subframe, and can betransmitted by identifying 8 antennas by the use of four subframesconfigured in this manner. For example, a CQI RS for antennas 0 and 1can be transmitted by performing CDM in a subframe n, and likewise, aCQI RS for antennas 2 and 3, a CQI RS for antennas 4 and 5, and a CQI RSfor antennas 6 and 7 can be transmitted by performing CDM respectivelyin subframes n+1, n+2, and n+3 (duty cycle 4).

FIG. 42 shows other examples for deploying a CQI RS to 8 resourceelements in two OFDM symbols in a subframe. A CQI RS can be deployed toconsecutive resource elements as shown in FIG. 42 (a). A CQI RS can bedeployed in a pattern in which two consecutive resource element pairsare spaced apart from each other as shown in FIG. 42 (b). A startposition of a resource element to which the CQI RS is deployed maydiffer for each cell.

FIG. 43 shows examples of deploying two CQI RSs to 8 resource elementsin two OFDM symbols in a subframe. Each CQI RS can be deployed to aresource element of the same frequency band in two OFDM symbols as shownin FIG. 43 (a), and can be deployed to a resource element of differentfrequency bands as shown in FIG. 43 (b).

If each of a CQI RS 1 and a CQI RS 2 are used in one antenna in onesubframe, two antennas can be identified and used, and 8 antennas can beused by using four subframes configured in this manner (duty cycle 4).Alternatively, if each of the CQI RS 1 and the CQI can be subjected toCDM to be able to identify two antennas in one subframe, 4 antennas canbe identified and used. If two subframes configured in this manner areused, 8 antennas can be identified (duty cycle 2). Alternatively, ifeach of the CQI RS 1 and the CQI RS 2 are subjected to CDM to be able toidentify 4 antennas in one subframe, 8 antennas can be identified (dutycycle 1).

FIG. 44 shows examples of deploying two CQI RSs to 8 resource elementsin two OFDM symbols in a subframe. FIG. 44 (a) shows an example in whicha CQI RS 1 and a CQI RS 2 are deployed to the same resource element (infrequency domain) in two OFDM symbols. FIG. 44 (b) shows an example inwhich CQI RSs are deployed to different resource elements in a frequencydomain. FIG. 44 (c) shows an example in which a CRI RS 1 and a CQI RS 2are deployed to the same resource element in a frequency domain, andeach CQI RS is deployed to resource elements which are spaced apart fromeach other by a distance of 6 resource elements. FIG. 44 (d) isdifferent from FIG. 44 (b) in a sense that each CQI RS is deployed toresource elements spaced apart from each other by a distance of 6resource elements. FIGS. 44 (e) and (f) are characterized in that onlyone CQI RS is deployed to one OFDM symbol. That is, an OFDM symbol towhich a CQI RS 1 is deployed is different from an OFDM symbol to which aCQI RS 2 is deployed.

FIG. 45 to FIG. 47 show examples of deploying four CQI RSs to 8 resourceelements in two OFDM symbols in a subframe.

The four CQI RSs deployed as shown in FIG. 45 to FIG. 47 can beidentified by being allocated (based on FDM) respectively to differentresource elements. A CQI RS 1 to a CQI RS 4 can use different basicsequences. The CQI RS 1 to the CQI RS 4 can be deployed by identifying 8antennas by the use of {CDM and TDM}.

For example, two resource elements to which the CQI RS 1 is deployed canbe subjected to CDM to be able to identify two antennas (e.g., antennas0 and 1), and two resource elements to which the CQI RS 2 is deployedcan also be subjected to CDM to be able to identify two antennas (e.g.,antennas 2 and 3). Likewise, CDM can be performed such that the CQI RS 3can identify antennas 4 and 5 and the CQI RS 4 can identify antennas 6and 7, thereby being able to two antennas for each CQI RS. That is, theCQI RS 1 to the CQI RS 4 are subjected to FDM, and each of the CQI RS 1to the CQI RS 4 can be subjected to CDM. In this case, the CQI RS forall of the 8 antennas can be transmitted in one subframe. A duty cyclemay be one subframe.

Alternatively, each of the CQI RS 1 to the CQI RS 4 can be transmittedas a CQI RS for one antenna in two resource elements in one subframe,and can be transmitted by identifying the 8 antennas by the use of twosubframes configured in this manner. For example, in a subframe n, theCQI RS 1 to the CQI RS 4 can be identified for antennas 0 to 3,respectively. In a subframe n+1, the CQI RS 1 to the CQI RS 4 can beidentified for antennas 4 to 7, respectively. That is, the CQI RS can betransmitted by performing TDM. In this case, a duty cycle may be twosubframes.

In FIG. 45, resource elements to which each CQI RS is deployed aredeployed by being spaced apart from each other by the same distance in afrequency domain. On the other hand, in FIG. 46, each CQI RS is deployedto 4 consecutive resource elements in a frequency domain. In FIG. 47,two CQI RSs are deployed to two consecutive resource elements in afrequency domain, and the remaining two CQI RSs are deployed to twoconsecutive resource elements located by being spaced apart from the twoconsecutive resource elements.

As shown in FIG. 46 (c) and FIG. 47 (c), two CQI RSs (i.e., CQI RS 1 andCQI RS 3) can be deployed to one OFDM symbol, and the remaining two CQIRSs (i.e., CQI RS 2 and a CQI RS 4) can be deployed to the remaining oneOFDM symbol. Alternatively, as shown in FIG. 45 to FIG. 47 and otherfigures, four CQI RSs can be deployed to one OFDM symbol.

As shown in FIG. 45 (a), FIG. 46 (a), and FIG. 47 (a), each CQI RS canbe deployed to the same resource element in a frequency domain in eachOFDM symbol, and as shown in other figure in FIG. 45 to FIG. 47, eachCQI RS can be deployed to different resource elements in a frequencydomain.

FIG. 48 shows an example in which a CQI RS is transmitted in two OFDMsymbols in a subframe and in which four CQI RSs are deployed to 8resource elements.

Referring to FIG. 48, each of two CQI RSs is deployed to two resourceelements in a resource region including one OFDM symbol in a time domainand 12 subcarriers in a frequency domain and two OFDM symbols configuredin this manner are included. A CQI RS 1 to a CQI RS 4 may use differentbasic sequences. The CQI RS 1 to the CQI RS 4 can be deployed byidentifying 8 antennas by the use of {CDM and TDM}.

For example, if each of the CQI RS 1 to the CQI RS 4 in one subframe isused for one antenna, 8 antennas can be identified by using twosubframes (duty cycle 2). Alternatively, if each of the CQI RS 1 to theCQI RS 4 in one subframe is subjected to CDM and is then used byidentifying two antennas, the 8 antennas can be identified by using onlyone subframe (duty cycle 1). Two resource elements to which the CQI RS 1is deployed can be subjected to CDM to be able to identify two antennas(e.g., antennas 0 and 1), and two resource elements to which the CQI RS2 is deployed can be subjected to CDM to be able to identify twoantennas (e.g., antennas 3 and 4). Likewise, each of the CQI RS 3 andthe CQI RS 4 can also be subjected to CDM to be able to identify twoantennas. That is, the CQI RS 1 to the CQI RS 4 can be subjected to FDM,and each of the CQI RS 1 to the CQI RS 4 can be subjected to CDM. Inthis case, the CQI RS for all of the 8 antennas can be transmitted inone subframe.

FIG. 49 shows another example in which a CQI RS is transmitted in twoOFDM symbols in a subframe and in which four CQI RSs are deployed to 8resource elements. In FIG. 49 (a), two CQI RSs are deployed to fourconsecutive resource elements. In FIG. 49 (b), two CQI RSs are deployedto two consecutive resource elements and another two consecutiveresource elements spaced apart by a specific resource element distance.A start position of a resource element to which the CQI RS is deployedmay be fixed, and may be shifted depending on an offset value. In FIG.49 (b), the offset value may be set to any one of values 1 to 4.

FIG. 50 and FIG. 51 show examples in which a CQI RS is transmitted intwo OFDM symbols in a subframe and in which 8 CQI RSs are deployed to 8resource elements.

Referring to FIG. 50, each of 8 CQI RSs is deployed to one resourceelement in a resource region including two OFDM symbols in a time domainand 12 subcarriers in a frequency domain. A CQI RS 1 to a CQI RS 8 canuse different basic sequences. Each of the CQI RS 1 to the CQI RS 8 canbe used for one antenna, thereby being able to identify 8 antennas.Resource elements to which a CQI RS is deployed can be located by beingspaced apart by the same resource element distance (i.e., a distance of3 resource elements). In FIG. 51 (a), a resource element to which theCQI RS 1 to the CQI RS 8 are deployed is located consecutively in afrequency domain. In this case, the CQI RS can be deployed by shiftingit by a distance of 4 resource elements in each cell so that a resourceelement to which the CQI RS is deployed in three contiguous cells doesnot overlap. In FIG. 51 (b), four CQI RSs are deployed to twoconsecutive resource elements and another two consecutive resourceelements spaced apart by a specific resource element distance, and thereare two OFDM symbols configured in this manner. In this case, the CQI RScan be deployed by shifting it by a distance of two resource elements ineach cell. Then, a resource element to which the CQI RS is deployed inthree contiguous cells can be prevented from overlapping.

FIG. 52 to FIG. 64 show examples in which a CQI RS is transmitted in twoOFDM symbols for a resource region including one subframe in a timedomain and 12 subcarriers in a frequency domain and in which 8 CQI RSsare deployed to 8 resource elements. As shown in the examples of FIGS.45 (a) to (d), FIGS. 46 (a) to (d), FIGS. 47 (a) to (d), FIG. 48, FIG.49, FIG. 50, FIG. 51, and FIG. 52 to FIG. 64, the CQI RSs can be locatedin specific two OFDM symbols in a subframe. FIG. 52 to FIG. 64 are forexemplary purposes only, and thus a start position on a frequency domainin which the CQI RS is deployed to specific two OFDM symbols can changevariously.

In frequency domain, resource elements to which a CQI RS is deployed maybe identical to resource elements to which a common RS is deployed (seeFIG. 52 to FIG. 56), or may be different (see FIG. 57 to FIG. 64).

As shown in the examples of FIG. 52 to FIG. 56, in case of a pattern inwhich CQI RSs are deployed by being spaced apart by the same resourceelement distance (i.e., a distance of 3 resource elements), a resourceelement to which the CQI RS is deployed in three contiguous cells can bedeployed by being shifted in a unit of one resource element to avoidoverlapping between resource elements. As shown in the examples of FIG.57 to FIG. 60, in case of a pattern in which CQI RSs are deployed tofour consecutive resource elements, a resource element to which the CQIRS is deployed in three contiguous cells can be deployed by beingshifted in a unit of four resource elements to avoid overlapping betweenresource elements. As shown in the examples of FIG. 61 to FIG. 64, incase of a pattern in which CQI RSs are deployed to two consecutiveresource elements and are deployed to two consecutive resource elementslocated by being spaced apart from the previous two consecutive resourceelements by a distance of 4 resource elements, a resource element towhich the CQI RS is deployed in three contiguous cells can be deployedby being shifted in a unit of two resource elements to avoid overlappingbetween resource elements.

FIG. 65 shows examples of deploying a CQI RS to 12 resource elements intwo OFDM symbols in a subframe. In one OFDM symbol, the CQI RS can bedeployed to resource elements spaced apart by the same resource elementdistance (i.e., a distance of two resource elements) as shown in FIG. 65(a), and can be deployed to 6 consecutive resource elements as shown inFIG. 65 (b). Alternatively, as shown in FIG. 65 (c) or FIG. 65 (d), theCQI RS can be deployed to a specific number of consecutive resourceelements and a specific number of consecutive resource elements spacedapart from the previous resource elements by a specific resource elementdistance. A resource element to which a CQI RS is deployed can beshifted in a frequency domain for each cell or cell group to reduceinterference between resource elements. For example, in case of FIG. 65(d), resource elements to which a CQI RS is deployed can be shifted in afrequency domain by setting an offset value to any one of values 1 to 8.

In case of FIG. 65 (a), 8 antennas can be identified by using CDM in onesubframe (duty cycle 1). Alternatively, four antennas can be identifiedby using CDM in one subframe, and 8 antennas can be identified by usingtwo subframes configured in this manner (duty cycle 2). Alternatively,two antennas can be identified by using CDM in one subframe, and 8antennas can be identified by using four subframes configured in thismanner (duty cycle 4).

FIG. 66 shows examples of deploying a CQI RS to 16 resource elements intwo OFDM symbols in a subframe.

In one OFDM symbol, a CQI RS can be deployed in a pattern in which twoconsecutive resource elements are spaced apart from each other by adistance of one resource element as shown in FIG. 66 (a), and a CQI RScan be deployed in a pattern in which four consecutive resource elementsare spaced apart by a distance of two resource elements as shown in FIG.66 (b). Alternatively, a CQI RS can be deployed to 8 consecutiveresource elements as shown in FIG. 66 (c).

For example, if a CQI RS is deployed as shown in FIG. 66 (a), 8 antennascan be identified by using CDM in one subframe (duty cycle 1). Fourantennas can be identified by using CDM in one subframe, and 8 antennascan be identified by using two subframes configured in this manner (dutycycle 2). 2 antennas can be identified by using CDM in one subframe, and8 antennas can be identified by using four subframes configured in thismanner (duty cycle 4).

FIG. 67 shows examples of deploying two CQI RSs to 16 resource elementsin two OFDM symbols in a subframe. Each CQI RS is deployed to 8 resourceelements.

A CQI RS 1 and a CQI RS 2 can be deployed to a resource element of thesame frequency domain in two OFDM symbols as shown in FIGS. 67 (a) and(c). Alternatively, as shown in FIG. 67 (b), CQI RSs can be deployed toresource elements of different frequency domains. FIG. 67 (d) shows anexample of deploying only one CQI RS to one OFDM symbol.

If each of two CQI RSs is used for one antenna in one subframe, foursubframes configured in this manner can be used to identify 8 antennas(duty cycle 4). If each CQI RS is used for two antennas in one subframeby using CDM, it can be used for four antennas. Therefore, two subframesconfigured in this manner can be used to identify 8 antennas (duty cycle2). If each CQI RS is used for four antennas in one subframe, only onesubframe can be used to identify 8 antennas (duty cycle 1).

FIG. 68 and FIG. 69 show other examples for deploying two CQI RSs to 16resource elements in two OFDM symbols in a subframe.

In the examples of FIG. 68 and FIG. 69, resource elements to which a CQIRS is deployed by an offset value can be used by being shifted in afrequency domain in a unit of cell or cell group. The offset value canbe set to any one of values 1 to 4.

FIG. 70 and FIG. 71 show examples for deploying four CQI RSs to 16resource elements in two OFDM symbols in a subframe.

If each CQI RS is used for one antenna in one subframe, four antennascan be identified, and thus two subframes configured in this manner canbe used to identify 8 antennas (duty cycle 2). Alternatively, a CQI RS 1to a CQI RS 4 deployed to one OFDM symbol in a subframe can be used toidentify four antennas, and a CQI RS 1 and a CQI RS 4 deployed to theremaining one OFDM symbol can be used to identify another four antennas(duty cycle 1). Alternatively, if each CQI RS in a subframe is used fortwo antennas by using CDM, four CQI RSs in the subframe can be used toidentify 8 antennas (duty cycle 1). In the examples of FIG. 71, resourceelements to which a CQI RS is deployed by an offset value can be used ina unit of cell or cell group by being shifted in a frequency domain. Theoffset value may be set to any one of values 1 to 6.

FIG. 72 and FIG. 73 show examples for deploying 8 CQI RSs to 16 resourceelements in two OFDM symbols in a subframe.

Since 8 CQI RSs are deployed in one subframe, 8 antennas can beidentified and used. Each CQI RS can be identified since a differentresource element is allocated thereto. In the examples of FIG. 73, aresource element to which a CQI RS is deployed can be shifted by 1 to 8resource elements in a frequency domain by an offset value. The offsetvalue may differ depending on a cell or cell group.

FIG. 74 shows an example in which a CQI RS is transmitted in two OFDMsymbols for a resource region including one subframe in a time domainand 12 subcarriers in a frequency domain and in which four CQI RSs aredeployed for 16 resource elements.

FIG. 75 shows an example in which a CQI RS is transmitted in two OFDMsymbols for a resource region including one subframe in a time domainand 12 subcarriers in a frequency domain and in which 8 CQI RSs aredeployed for 16 resource elements.

The present invention can be implemented with hardware, software, orcombination thereof. In hardware implementation, the present inventioncan be implemented with one of an application specific integratedcircuit (ASIC), a digital signal processor (DSP), a programmable logicdevice (PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, other electronic units, and combinationthereof, which are designed to perform the aforementioned functions. Insoftware implementation, the present invention can be implemented with amodule for performing the aforementioned functions. Software is storablein a memory unit and executed by the processor. Various means widelyknown to those skilled in the art can be used as the memory unit or theprocessor.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

The invention claimed is:
 1. A method for transmitting a referencesignal in a multi-antenna system, the method comprising: allocating atleast one reference signal capable of measuring a channel state for eachantenna in a subframe containing a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols; and transmitting the allocated atleast one reference signal, wherein each of the at least one referencesignal is allocated to two resource elements in two OFDM symbols of thesubframe, and wherein two reference signals for two antennas aretransmitted through same two resource elements and the two referencesignals transmitted through the same two resource elements areidentified by codes which are different from each other.
 2. The methodof claim 1, wherein the two OFDM symbols are consecutive in a timedomain.
 3. The method of claim 1, wherein a reference signal for oneantenna is transmitted through two resource elements, which have thesame frequency, in the two OFDM symbols.
 4. The method of claim 1,wherein reference signals for a first antenna and a second antenna aretransmitted through two resource elements having a first frequency inthe two OFDM symbols, and reference signals for a third antenna and afourth antenna are transmitted through two resource elements having asecond frequency in the two OFDM symbols.
 5. The method of claim 4,wherein the reference signals for the first and the second antenna areidentified by different codes, and the reference signals for the thirdantenna and the fourth antenna are identified by different codes.
 6. Themethod of claim 1, wherein reference signals for a first antenna and asecond antenna are transmitted through two resource elements having afirst frequency in the two OFDM symbols, reference signals for a thirdantenna and a fourth antenna are transmitted through two resourceelements having a second frequency in the two OFDM symbols, referencesignals for a fifth antenna and a sixth antenna are transmitted throughtwo resource elements having a third frequency in the two OFDM symbols,and reference signals for a seventh antenna and a eighth antenna aretransmitted through two resource elements having a fourth frequency inthe two OFDM symbols.
 7. The method of claim 6, wherein two referencesignals transmitted through the same two resource elements areidentified by different codes.
 8. The method of claim 6, wherein the tworesource elements having the first frequency and the two resourceelements having the third frequency are consecutive in a frequencydomain.
 9. The method of claim 8, wherein the two resource elementshaving the second frequency and the two resource elements having thefourth frequency are consecutive in a frequency domain.
 10. The methodof claim 1, wherein the two OFDM symbols are included in a first slot ora second slot of the subframe.
 11. A method for receiving a referencesignal in a multi-antenna system, the method comprising: receiving atleast one reference signal capable of measuring a channel state for eachantenna in a subframe containing a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols; and measuring a channel state foreach antenna, wherein each of the at least one reference signal isallocated to two resource elements in two OFDM symbols of the subframe,and wherein two reference signals for two antennas are received throughsame two resource elements and the two reference signals receivedthrough the same two resource elements are identified by codes which aredifferent from each other.